Device Shadow Service for AWS IoT

A device's shadow is a JSON document that is used to store and retrieve current state
information for a device. The Device Shadow service maintains a shadow for each device
you connect to AWS IoT. You
can use the shadow to get and set the state of a device over MQTT or HTTP, regardless
of whether the device is
connected to the Internet. Each device's shadow is uniquely identified by the name
of the corresponding
thing.